Locke's Letter Concerning Toleration, watershed of political theory that it is, arguably marks the point where mention of religion and, as a result, what used to count as morality started getting swept out of the public sphere and, ultimately, into the void. Private religion being an oxymoron. So I had to rub my eyes when I picked it up to see this on its opening pages:

Now, though the divisions that are amongst sects should be allowed to be never so obstructive of the salvation of souls; yet, nevertheless, adultery, fornication, uncleanliness, lasciviousness, idolatry, and such-like things, cannot be denied to be works of the flesh, concerning which the apostle has expressly declared that "they who do them shall not inherit the kingdom of God." Whosoever, therefore, is sincerely solicitous about the kingdom of God and thinks it his duty to endeavour the enlargement of it amongst men, ought to apply himself with no less care and industry to the rooting out of these immoralities than to the extirpation of sects. But if anyone do otherwise, and whilst he is cruel and implacable towards those that differ from him in opinion, he be indulgent to such iniquities and immoralities as are unbecoming the name of a Christian, let such a one talk never so much of the Church, he plainly demonstrates by his actions that it is another kingdom he aims at and not the advancement of the kingdom of God.